Writing implement

ABSTRACT

A writing implement including a plurality of component parts A, B, C, etc. is satisfactory in balance and stability during writing operations and can be smoothly handled for minute, reciprocating, turning motions during writing operations. The writing implement including the component parts A, B, C etc. has its center of gravity in a part thereof between a position at 20 mm from the tip of a projected writing element and a position corresponding to the middle of the overall length thereof, and the weight of the part thereof between the position at 20 mm from the tip of the projected writing element and the position corresponding to the middle of the overall length is not less than 50% of the total weight of the writing implement.

TECHNICAL FIELD

The present invention relates to a writing implement including aplurality of writing parts.

BACKGROUND ART

Techniques relating to the center of gravity of a writing implement havebeen proposed. For example, a writing implement disclosed in JP2001-270281 A (Patent document 1) having its center of gravity in amiddle region of a barrel having front, middle and back regions andcapable of being stably handled in minute, reciprocating, turningmotions for writing.

The inventors of the present invention made studies to develop a writingimplement that can be easily handled in minute, reciprocating, turningmotions and found that a writing implement makes minute, reciprocating,turning motions to move its writing point up and down as shown in FIG. 3when the writing point is shifted from the end of the last stroke of oneletter to a position to start writing the next letter. A writingimplement capable of being easily handled in minute, reciprocating,turning motions has an axis of turning passing corresponding to orsubstantially corresponding to its center of gravity. It is inferredthat such a writing implement can be easily handled in reciprocating,turning motions because the writing implement has a small rotationalinertia about the axis of turning.

The center of gravity of the writing implement disclosed in JP2001-270281 A including the barrel having the front, the middle and theback region can be set in the middle region by taking into considerationthe total weight of the writing implement and the respective weights ofthe component parts. However, the writing implement constructed simplyso that the center of gravity is in the middle region of the barrelcould not give a hand gripping the writing implement satisfactorysensation of balance and stability.

A writing implement designed to place the center of gravity in itsmiddle region, ignoring weight distribution is not necessarily capableof being satisfactorily handled in minute, reciprocating, turningmotions.

A region denoted by the term “middle region” in Patent document 1extends from a range having diameter decreasing in a curve from a frontend toward a middle part to a range having diameter decreasing in acurve from the back end toward the middle part. According to thedefinition of the term “middle region”, the middle region could be apart near the tip of the writing implement or near the push button,depending on the shape of the writing implement. Thus, the position ofthe middle region defined by this term is very vague and hence theconception of weight distribution cannot be introduced into the writingimplement mentioned in Patent document 1.

If weight distribution is ignored and an attention is paid only to theposition of the center of gravity, the center of gravity can be set inthe middle region even if front and back parts of the writing implementare formed from metallic parts. However, such a writing implement isill-balanced and is unable to give a satisfactory sensation of stabilityto the hand gripping the writing implement. When the writing implementis gripped by a hand in a tilted position for writing, the metallicparts respectively having high specific weights destroy the balance andspoil the stability of the writing implement. When the front and theback part remote from the center of gravity are formed from metallicparts respectively having high specific weights, the writing implementhas a large rotational inertia and cannot be smoothly operated inminute, reciprocating, turning motions.

As generally known, rotational inertia indicates the degree ofdifficulty in starting a body for rotation and the degree of difficultyin stopping a rotating body. Generally, it is easier to turn a straightbar about an axis passing the center of the straight bar than turningthe same straight bar about an axis passing one of its ends because thediameter of a circle followed by an end of the straight bar when thestraight bar is turned about the axis passing the center of the straightbar is smaller than that of a circle flowed by one of the ends of thestraight bar when the straight bar is turned about the axis passing theother end of the straight bar. Thus, the position of the center ofgravity of a body is closely related with the rotational inertia of thebody; the rotational inertia of the body is the least if the axis ofrotation passes the center of gravity of the body and the rotationalinertia increases with the distance of the axis of rotation from thecenter of gravity.

Therefore, the rotational inertia can be reduced by making the axis ofrotation pass the center of gravity. However, it was found that facilityof handling the writing implement in minute, reciprocating, turningmotions cannot be improved simply by setting the axis of turning of thewriting implement at the center of gravity because the writing implementconsists of many component parts and the rotational inertia of thewriting implement is the sum of the respective rotational inertias ofthe component parts.

The least rotational inertia of a writing implement can be expressed by:I=dI ₁ +dI ₂ +dI ₃ + . . . +dI _(n)where I is the minimum rotational inertia of the writing implement, dI₁,dI₂, dI₃, . . . are the rotational inertias of the component parts A, B,C, etc. about an axis of rotation passing the center of gravity of thewriting implement.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to solve problemsin the foregoing prior art and to provide a writing implementwell-balanced and capable of giving a satisfactory sensation ofstability to the hand gripping the writing implement, of being handledin smooth, minute, reciprocating, turning motions for a satisfactorywriting operation.

The inventors of the present invention studied the balance and stabilityof writing implements during writing operations and have found that ahand grips a writing implement by placing the tips of the thumb, thefirst finger and the second finger on a part a of the writing implementand resting a part b of the writing implement at the joint of the thumband the first finger as shown in FIG. 14, and the writing implementgives satisfactory sensations of balance and stability during writingoperations if the writing implement has its center of gravity at a pointbetween the parts a and b and the most part of the weight of the writingimplement is concentrated on a part of the writing implement between theparts a and b.

Generally, a writing implement with a projecting writing element, suchas a mechanical pencil, a ballpoint pen, a fountain pen or a marker, hasa length between 120 and 180 mm and the tip part of the writingimplement is tapered to facilitate seeing the tip of the writingelement. Therefore, the part a on which the tips of the thumb, the firstfinger and the second finger are placed is behind the tapered tip part.Although different writing implements have tip parts of differentshapes, respectively, the length of the tip part including the writingelement is between about 15 and about 20 mm and hence the part a is at adistance between 15 and 20 mm backward from the tip of the writingelement. Although dependent on the size of the hand gripping the writingimplement, the part b that rests on the joint of the thumb and the firstfinger is at least a short distance behind the middle part of thewriting implement. Consequently, the writing implement is able to givesatisfactory sensations of balance and stability when the writingimplement has its center of gravity at a position between a part at 20mm from the tip of the writing element and the middle part and hasweight concentrated on a part near the center of gravity.

The present invention has been made on the basis of the foregoingknowledge acquired by the inventors of the present invention. A writingimplement according to the present invention including component partsA, B, C, etc. is characterized in that its center of gravity is at aposition between a position at 20 mm from the tip of a projected writingelement and a position corresponding to the middle of the overall lengththereof, and the weight of a part between the position at 20 mm from thetip of the projected writing element and the position corresponding tothe middle of the overall length thereof is not less than 50% of thetotal weight thereof.

The writing implement is characterized in that the center of gravity isat a position between the middle of a part between the position at 20 mmfrom the tip of the writing element and the position corresponding tothe middle of the overall length thereof and the middle of the overalllength thereof.

The writing implement is characterized by a weight adjusting part placedin a part between the position at 20 mm from the tip of the writingelement and the position corresponding to the middle of the overalllength thereof.

The writing implement is characterized in that the weight adjusting partis formed of a metal.

The writing implement is characterized in that a tip part and/or a backpart thereof is formed of a metal having a low specific gravity or aresin having a low specific gravity.

The writing implement is characterized in that the tip part and/or theback part is formed of a metal or a resin having a specific gravitylower than the specific gravity of a part between the position at 20 mmfrom the tip of the writing element and the position corresponding tothe middle of the overall length thereof.

The writing implement is characterized in that the total weight of thecomponent parts A, B, C, etc. is 15 gf or above.

The writing implement is characterized in having a rotational inertiabetween 4,300 and 25,000 gf·mm² about an axis passing the center ofgravity.

The writing implement is characterized in having a rotational inertia of20,000 gf·mm² or below about an axis passing the center of gravity.

Possible metals having a low specific gravity are those having aspecific gravity lower than that of brass, such as aluminum (specificgravity: 2.7 gf/cm³), aluminum alloys magnesium (specific gravity: 1.74gf/cm³), and magnesium alloys. Possible resins having a low specificgravity are those having a specific gravity below 1.0 gf/cm³ and lowerthan those of polycarbonate resins, such as polypropylene resins(specific gravity: 0.90 to 0.91 gf/cm³ and/or polyethylene resins(specific gravity: 0.91 to 0.97 gf/cm³).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a writing implement in afirst embodiment according to the present invention;

FIG. 2 is a diagram showing weight distribution in the writing implementshown in FIG. 1;

FIG. 3 is a view of assistance in explaining the minute, reciprocating,turning motions of a writing implement;

FIG. 4 is a longitudinal sectional view of a writing implement in asecond embodiment according to the present invention;

FIG. 5 is a diagram showing weight distribution in the writing implementshown in FIG. 3;

FIG. 6 is a longitudinal sectional view of a writing implement in athird embodiment according to the present invention;

FIG. 7 is a diagram showing weight distribution in the writing implementshown in FIG. 6;

FIG. 8 is a longitudinal sectional view of a conventional push-buttonwriting implement;

FIG. 9 is a diagram showing weight distribution in the push-buttonwriting implement shown in FIG. 8;

FIG. 10 a longitudinal sectional view of a conventional capped writingimplement;

FIG. 11 is a diagram showing weight distribution in the capped writingimplement shown in FIG. 10;

FIG. 12 is a longitudinal sectional view of a pencil;

FIG. 13 is a diagram showing weight distribution in the pencil shown inFIG. 12; and

FIG. 14 is a pictorial view of assistance in explaining a mode ofgripping a writing implement for writing by placing the tips of thethumb, the first finger and the second finger on a part a and resting apart b at the joint of the thumb and the first finger.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described withreference to the accompanying drawings, in which the same parts andpositions are denoted by the same reference characters.

Referring to FIG. 1 showing a writing implement 1 in a first embodimentaccording to the present invention, a barrel 2 of a polypropylene resin,i.e., a resin having a low specific gravity, has a reduce gripping partof an outside diameter smaller than that of other parts. A grip member 4of a silicone rubber having a high specific gravity of about 1.2 gf/cm³is put on the gripping part of the barrel 2. this writing implement 1 isa push-button ballpoint pen. A barrel cap 3 formed of a PC resin(polycarbonate resin) is screwed in the front end of the barrel 2. Aballpoint pen refill is inserted in the barrel 2 and is pushed backwardby a coil spring formed by coiling a hard steel wire. The ballpoint penrefill has a cartridge tube 7 of a PP resin (polypropylene resin)containing an oil ink, and a ballpoint pen tip 8 having a socketrotatably holding a tungsten carbide ball and attached to the front endof the cartridge tube 7.

The barrel 2 is provided in its inner surface with a cam groove, notshown, for guiding a rotary cam 5 formed of a POM resin(polyoxymethylene resin) for axial movement and for turning. Aprojection formed on the rotary cam 5 is engaged in the cam groove. Apush button 6 formed of a PC resin is inserted in a back part of thebarrel 2 so as to project partly from the back end of the barrel 2. Thepush button 6 has a cam part for axially moving and turning the rotarycam 5 in its front part. A clip 9 is formed integrally with a back partof the barrel 2.

The writing implement is 13.6 gf in total weight and 140 mm in overalllength with the ballpoint tip 8 projected from the front end of thebarrel cap 3, i.e., with the ballpoint tip set at a writing position.The center of gravity of the push-button writing implement is at aposition at 67.8 mm from the writing point. The push-button writingimplement has a rotational inertia I of about 20,000 gf·mm² about anaxis passing the center of gravity perpendicularly to the axis of thebarrel 2.

The weight of the writing implement is distributed in a weightdistribution curve shown in FIG. 2 when the writing implement is set ina writing condition with its writing element projected. The grip member4 is formed of the elastic material having a high specific gravity in abig thickness so that the weight of a part of the writing implementbetween a position at 20 mm from the writing point and a position at themiddle of the overall length is not less the 50% of the total weight ofthe writing implement. More concretely, the weight of the part of thewriting implement between the position at 20 mm from the writing pointand the position at the middle of the overall length, i.e., a front halfof 70 mm in length measured from the writing point of the writingimplement is 7.0 gf, which is about 51% of the total weight of thewriting implement. The writing implement is sliced in 1 mm thick slices,the weight of each slice is determined by adding up the respectiveweights of parts of the component parts included in the slice.

Referring to FIG. 3, the writing implement makes minute, reciprocating,turning motions to move its writing point up and down when the writingpoint is shifted from the end of the last stroke of one letter to aposition to start writing the next letter. It is generally known thatthe writing implement turns for this turning motion about an axis K ofturning passing a position substantially corresponding to the middle ofthe writing implement. The writing implement in the first embodiment isbuilt such that its center of gravity is at a position between theposition at 20 mm from the writing point and the position correspondingto the middle of the overall length of the writing implement,preferably, at a position between the middle of a part between theposition at 20 mm from the writing point and the position correspondingto the middle of the overall length thereof, and the middle of theoverall length thereof. Since the center of gravity is not far apartfrom the position approximately corresponding to the middle of thewriting implement and the axis K is near the center of gravity, therotational inertia of the writing implement in use is small.Consequently, the writing implement can be smoothly operated in minute,reciprocating, turning motions for satisfactory writing operation.

A writing implement 11 in a second embodiment according to the presentinvention shown in FIG. 4 is a push-button ballpoint pen of constructionsimilar to that of the writing implement in the first embodiment, exceptthat the writing implement 11 has a barrel 2 having a gripping partprovided with a grip member 14 and a weight adjusting part G. The weightadjusting part G is put on a part of the barrel 2 between a position at20 mm from the writing point and a position corresponding to the middleof the overall length of the writing implement 11. The total weight ofthe writing implement 11 is 20.8 gf. The weight adjusting part G isformed of brass having a high specific gravity of about 8.3 gf/cm³ andhas a weight of 8.4 gf. The weight adjusting part G is the heaviestamong the component members of the writing implement 11. The weightadjusting part G has a cylindrical shape and is covered with andconcealed by the grip member 14. The writing implement 11 is 140 mm inoverall length and has its center of gravity at a position at 64.3 mmfrom its writing point and a rotational inertia I of about 12,000 gf·mm²about an axis passing the center of gravity perpendicularly to the axisthereof.

The weight adjusting part G dominates the weight of the writingimplement 11. The weight adjusting part G is effective in localizingmost part of the weight of the writing implement 11 in a part of thewriting implement 11 between the position at 20 mm from the writingpoint and the position at the middle of the overall length of thewriting implement 11, preferably, in a part between the middle of a partbetween the position at 20 mm from the writing point and the positioncorresponding to the middle of the overall length thereof, and themiddle of the overall length thereof. The weight adjusting part G may beplaced inside the barrel 2 and may be any suitable shape other than thecylindrical shape, provided that the weight adjusting part G is placedin a part of the writing implement 11 between the position at 20 mm fromthe writing point and the position at the middle of the overall lengthof the writing implement 11. The writing implement 11 provided with theweight adjusting part G has a desired weight, has a small rotationalinertia and can be smoothly handled in minute, reciprocating, turningmotions for a satisfactory writing operation.

The weight of the writing implement 11 is distributed in a weightdistribution curve shown in FIG. 5. The metallic weight adjusting part Gis disposed such that the weight of a part between a position at 20 mmfrom the writing point and a position corresponding to the middle of theoverall length of the writing implement 11, i.e., a position at 70 mmfrom the writing point, is not less than 50% of the total weight of thewriting implement 11. More concretely, the weight of the part betweenthe position at 20 mm from the writing point and the positioncorresponding to the middle of the overall length of the writingimplement 11, i.e., the position at 70 mm from the writing point, is13.9 gf, which is about 67% of the total weight of the writing implement11.

A writing implement 21 in a third embodiment according to the presentinvention shown in FIG. 6 is a capped ballpoint pen. The writingimplement 21 has a barrel 22 having a gripping part, a grip member 24put on the gripping part of the barrel 22, a weight adjusting part G′put on the gripping part of the barrel 22 to localize most part of theweight of the writing implement 21 in a part between a position at 20 mmfrom a writing point and a position corresponding to the middle of theoverall length of the writing implement 21, and a cap 25 integrallyprovided with a clip 26 and put on a back part of the barrel 2. Theweight adjusting part G′ is formed of aluminum of about 2.7 gf/cm³ inspecific gravity. the cap 25 is formed of a polypropylene resin. Thewriting implement 21 is 17.1 gf in total weight and 140 mm in overalllength. The writing implement 21 has its center of gravity at a positionat 67.4 mm from the writing point and a rotational inertia I of about26,000 gf·mm² about an axis passing the center of gravityperpendicularly to the axis of the writing implement 21.

The weight of the writing implement 21 is distributed in a weightdistribution curve shown in FIG. 6. The weight of a part between aposition at 20 mm from the writing point and a position corresponding tothe middle of the overall length of the writing implement 21, i.e., aposition at 70 mm from the writing point, is 9.8 gf, which is about 58%of the total weight of the writing implement 21.

FIG. 8 shows a conventional push-button ballpoint pen (writingimplement) 101 similar in construction to the writing implements in thefirst and the second embodiment. The push-button ballpoint pen 101 has abarrel cap 103 formed of brass, a barrel 2 not provided with any weightadjusting member, and an elastic tube 104 formed of a silicone rubber ina small thickness and put on the barrel 2. The weight of the push-buttonballpoint pen 101 is distributed in a weight distribution curve shown inFIG. 9. The push-button ballpoint pen 101 has its center of gravity at aposition at 54.9 mm from the writing point, and the weight of a partbetween a position at 20 mm from the writing point and a positioncorresponding to the middle of the overall length thereof, i.e., aposition at 70 mm from the writing point, is about 31% of the totalweight of the push-button ballpoint pen 101, i.e., a weight not greaterthan 50% of the total weight of the push-button ballpoint pen 101.

More concretely, the push-button ballpoint pen 101 is 16.2 gf in totalweight and 140 mm in overall length and has its center of gravity at aposition at 54.9 mm from the writing point and a rotational inertia I ofabout 30,000 gf·mm² about an axis passing the center of gravityperpendicularly to the axis of the push-button ballpoint pen 101. Theweight of the part of the push-button ballpoint pen 101 between theposition at 20 mm from the writing point and the position correspondingto the middle of the overall length of the push-button ballpoint pen101, i.e., the position at 70 mm from the writing point, is 5.0 gf,which is about 31% of the total weight of the push-button ballpoint pen101.

FIG. 10 shows a conventional capped ballpoint pen (writing implement)121. The capped ballpoint pen 121 has a barrel cap 103 formed of brasssimilar to that of the writing implement in the third embodiment and acap 125 of a PC resin integrally provided with a clip 126, and does nothave any member corresponding to the weight adjusting part. The weightof the capped ballpoint pen 121 is distributed in a weight distributioncurve shown in FIG. 11. The weight of a part between a position at 20 mmfrom the writing point and a position corresponding to the middle of theoverall length of the capped ballpoint pen 121, i.e., a position at 70mm from the writing point, 5.0 gf, which is about 28% of the totalweight of the capped ballpoint pen 121 i.e., a weight not greater than50% of the total weight of the capped ballpoint pen 121.

More concretely, the capped ballpoint pen 121 is 17.9 gf in total weightand 140 mm in overall length and has its center of gravity at a positionat 63.4 mm from the writing point and a rotational inertia I of about41,000 gf·mm² about an axis passing the center of gravityperpendicularly to the axis of the push-button ballpoint pen 121. Theweight of the part of the capped ballpoint pen 121 between the positionat 20 mm from the writing point and the position corresponding to themiddle of the overall length of the capped ballpoint pen 121, i.e., theposition at 70 mm from the writing point, is 5.0 gf, which is about 38%of the total weight of the capped ballpoint pen 121.

The writing implements in the first and the second embodiment weretested for balance and stability during writing operations in comparisonwith the conventional push-button writing implement, and the writingimplement in the third embodiment was tested for balance and stabilityduring writing operations in comparison with the conventional cappedwriting implement. The balance and stability of the test writingimplements during writing operations were evaluated by one hundredtesters (seventy male testers and thirty female testers) of ages betweenthe tens and the fifties. The test writing implements of the presentinvention superior in balance and stability to the conventional writingimplements were marked with a double circle, the test writing implementsof the present invention equal in balance and stability to theconventional writing implements were marked with a circle, and the testwriting implement of the present invention not superior in balance andstability to the conventional writing elements were marked with a cross.The writing implements marked with a double circle, those marked with acircle and those marked with a cross were about 60%, about 30% and about10%, respectively, of the test writing implements of the presentinvention.

In selecting materials for forming the component parts of theconventional writing implement, importance is attached to hardness andstrength or matters dominating appearance, such as transparency.Although the position of the center of gravity of the conventionalwriting implement is specified in designing the conventional writingimplement, any attention is not paid to weight distribution and,particularly, the weight of a part of the writing implement between aposition at 20 mm from the writing point and a position corresponding tothe middle of the overall length of the writing implement is not takeninto consideration in designing the conventional writing implement. Forexample, the elastic member of the conventional writing implement isformed of a silicone rubber having a large specific weight between 1.0and 1.3 gf/cm³, whereas the barrel cap and/or the back end part isformed of a polycarbonate resin having a large specific weight of 1.2gf/cm³ or a metal such as copper or iron or the barrel cap and/or a backpart is formed of a polypropylene resin having a small specific weightbetween 0.90 and 0.91 gf/cm³, whereas the elastic member is formed of apolyolefin elastomer having a small specific weight of 0.88 gf/cm³.Consequently, the part of the writing implement between the position at20 mm from the writing point and the position corresponding to themiddle of the overall length of the writing implement cannot be formedin a weight not smaller than 50% of the total weight of the writingimplement.

FIG. 12 shows a sharpened pencil ready for writing. The pencil is 3.2 gfin total weight and 140 mm in overall length and has its center ofgravity at a position at 76.5 mm from its tip and a rotational inertia Iof about 4,300 gf·mm² about an axis passing the center of gravityperpendicularly to the axis thereof. The weight of the pencil isdistributed in a weight distribution curve shown in FIG. 13. The weightof the pencil excluding the sharpened front part is distributeduniformly. The weight of a part between a position at 20 mm from the tipand a position corresponding to the middle of the overall length of thewriting implement 21, i.e., a position at 70 mm from the tip, is 1.3 gf,which is about 40% of the total weight of the pencil.

A writing implement having uniformly distributed weight represented by apencil is light and hence has a small rotational inertia. However, theweight of a part of the writing implement between a part bon which thetips of the thumb, the first finger and the second finger are placed anda part resting on a part at the joint of the thumb and the first finger,i.e., a part between a position at 20 mm from the tip and a positioncorresponding to the middle of the overall length of the writingimplement, is not equal to or greater than 50% of the total weight ofthe writing implement and hence the writing implement is unsatisfactoryin balance and stability during writing operations.

It is essential to the present invention that the weight of a part of awriting implement between a position at 20 mm from the writing point anda position corresponding to the middle of the overall length of thewriting implement is not smaller than 50% of the total weight of thewriting implement. Therefore, it is desirable that the writing implementof the present invention has a gripping part provided with an elasticmember and a weight adjusting member and includes other component partsformed of resins each having a low specific gravity to adjust the wallthickness of the component parts and to take into consideration thedistribution of the respective weights of the other component parts.

When the weight of a part of a writing implement between a position at20 mm from the writing point and a position corresponding to the middleof the overall length of the writing implement is not smaller than 50%of the total weight of the writing implement, the writing implementgives a hand gripping the writing implement a satisfactory sensation ofbalance and stability, the rotational inertia of the writing implementis small and the writing implement can be smoothly handled for minute,reciprocating, turning motions. If the weight of a part of a writingimplement between a position at 20 mm from the writing point and aposition corresponding to the middle of the overall length of thewriting implement is less than 50% of the total weight of the writingimplement, it is possible that a front part other than the part betweenthe position at 20 mm from the writing point and the positioncorresponding to the middle of the overall length of the writingimplement or a rear part is heavy and it is possible that the writingimplement is ill-balanced during writing operations.

As mentioned above, there is not any particular restrictions on theconstruction of the writing implement of the present invention, providedthat the weight of a part of the writing implement between a position at20 mm from the writing point and a position corresponding to the middleof the overall length of the writing implement is not smaller than 50%of the total weight of the writing implement. The center of gravity ofthe writing implement can be easily set at a position in and a weightnot less than 50% of the total weight of the writing implement can beeasily distributed in the part of the writing implement between aposition at 20 mm from the writing point and a position corresponding tothe middle of the overall length of the writing implement by weightingthe part of the writing implement between a position at 20 mm from thewriting point and a position corresponding to the middle of the overalllength of the writing implement.

A comparatively heavy writing implement of 15 gf or above in totalweight can give a pleasant weighty sensation as compared with acomparatively light writing implement of a weight on the order of 10 gfincluding most of the component parts formed of resins. Since the frontpart including the barrel cap and a knob and/or a back part of theconventional writing implement is formed of a metal having a highspecific gravity, such as brass or iron, to form the writing implementin a comparatively large weight, it is difficult to set the center ofgravity of the writing implement at a position in and to distribute aweight not less than 50% of the total weight of the writing implement inthe part of the writing implement between a position at 20 mm from thewriting point and a position corresponding to the middle of the overalllength of the writing implement. Thus, the constitution and effect ofthe present invention worth appreciation.

If a component member distant from the axis of turning of theconventional writing implement not satisfactory in balance and stabilityduring writing operations and incapable of smoothly achieving minute,reciprocating, turning motions passes the center of gravity is formed ofa metal having a large specific weight, such as brass or iron, thewriting implement has a large rotational inertia. For example, a heavyconventional writing implement of 15 gf or above in total weight has arotational inertia not smaller than 20,000 gf·mm². The rotationalinertia of a writing implement satisfactory in balance and stabilityduring writing operations and capable of smoothly achieving minute,reciprocating, turning motions must be less than 30,000 gf·mm². Awriting implement having a rotational inertia not greater than 25,000gf·mm² is able to exhibit the effect of the present invention.Preferably, a writing implement according to the present invention has arotational inertia not greater than 20,000 gf·mm². Such a writingimplement is able to exhibit the effect of the present invention moreeffectively.

The smaller the rotational inertia of the writing implement, the betteris the turning performance of the writing implement in minute,reciprocating, turning motions and the easier to stop. The rotationalinertia of a pencil is as small as about 4,300 gf·mm². If a writingimplement has a rotational inertia less than 4,300 gf·mm², the writingimplement looks cheap and lightweight even if the writing implement isformed in a large weight of 15 gf or above greater than those of cheapwriting implements. Therefore, it is desirable to form a writingimplement so that 4,300 gf·mm²≦I≦25,000 gf·mm², preferably 4,300gf·mm²≦I<20,000 gf·mm², where I is the rotational inertia of the writingimplement.

A part of a writing implement between a position at 20 mm from thewriting point of the writing implement and a position corresponding tothe middle of the overall length of the writing implement can be easilyformed in a weight not less than 50% of the total weight of the writingimplement and the weight of the writing implement can be easilydistributed such that most part of the weight is distributed around thecenter of gravity of the writing implement by forming a component partin a front part of the writing implement and/or a component part in aback part of the writing implement of a metal having a low specificgravity or a resin having a low specific gravity. Since the componentpart formed of a metal having a low specific gravity or a resin having alow specific gravity is in the front part and/or the back part of thewriting implement and is distant from the center of gravity, the effectof the component part on increasing the rotational inertia of thewriting implement is insignificant and hence the rotational inertia ofthe writing implement is small.

Although the push-button ballpoint pen provided with the rotary cam andthe capped ball-point pent have been described by way of example, theconstruction of the writing tip and the ink are not limited to thosespecifically described herein. The present invention is applicable alsoto push-button writing implements and capped writing implements ofconstruction other than that specifically described herein. The cappedwriting implement is expected to be used for writing with its cap put onits back part. The position of the center of gravity and the totalweight of the capped writing implement is determined in a state wherethe cap is put on the back part of the capped writing implement. Thepresent invention can be particularly effectively applied to thepush-button writing implement with the rotary cam as mentioned abovebecause many component parts including the rotary cam and the pushbutton are arranged in a back part of the barrel.

The writing implement according to the present invention is satisfactoryin balance and stability during writing operations and is capable ofbeing smoothly handled for minute, reciprocating, turning motions duringwriting motions.

1. A writing implement comprising component parts A, B, C, etc.,characterized in that its center of gravity is at a position between aposition at 20 mm from the tip of a projected writing element and aposition corresponding to the middle of the overall length thereof, andthe weight of a part between the position at 20 mm from the tip of theprojected writing element and the position corresponding to the middleof the overall length thereof is not less than 50% of the total weightthereof.
 2. The writing implement according to claim 1 characterized inthat the center of gravity is at a position between the middle of a partbetween the position at 20 mm from the tip of the writing element andthe position corresponding to the middle of the overall length thereofand the middle of the overall length thereof.
 3. The writing implementaccording to claim 1 characterized in that a weight adjusting member isplaced in a part between the position at 20 mm from the tip of thewriting element and the position corresponding to the middle of theoverall length.
 4. The writing implement according to claim 3characterized in that the weight adjusting part is formed of a metal. 5.The writing implement according to claim 1 characterized in that a tippart and/or a back part of the writing implement is formed of a metalhaving a low specific gravity or a resin having a low specific gravity.6. The writing implement according to claim 5 characterized in that thetip part and/or the back part is formed of a metal or a resin having aspecific gravity lower than the specific gravity of a part between theposition at 20 mm from the tip of the writing element and the positioncorresponding to the middle of the overall length.
 7. The writingimplement according to claim 1 characterized in that the total weight ofthe component parts A, B, C, etc. is 15 gf or above.
 8. The writingimplement according to claim 1 characterized in having a rotationalinertia between 4,300 and 25,000 gf·mm² about an axis passing the centerof gravity.
 9. The writing implement according to claim 8 characterizedin that the rotational inertia about the axis passing the center ofgravity is 20,000 gf·mm² or below.
 10. The writing implement accordingto claim 2 characterized in that a weight adjusting member is placed ina part between the position at 20 mm from the tip of the writing elementand the position corresponding to the middle of the overall length. 11.The writing implement according to claim 10 characterized in that theweight adjusting part is formed of a metal.
 12. The writing implementaccording to claim 2 characterized in that a tip part and/or a back partof the writing implement is formed of a metal having a low specificgravity or a resin having a low specific gravity.
 13. The writingimplement according to claim 3 characterized in that a tip part and/or aback part of the writing implement is formed of a metal having a lowspecific gravity or a resin having a low specific gravity.
 14. Thewriting implement according to claim 10 characterized in that a tip partand/or a back part of the writing implement is formed of a metal havinga low specific gravity or a resin having a low specific gravity.
 15. Thewriting implement according to claim 4 characterized in that a tip partand/or a back part of the writing implement is formed of a metal havinga low specific gravity or a resin having a low specific gravity.
 16. Thewriting implement according to claim 11 characterized in that a tip partand/or a back part of the writing implement is formed of a metal havinga low specific gravity or a resin having a low specific gravity.
 17. Thewriting implement according to claim 12 characterized in that the tippart and/or the back part is formed of a metal or a resin having aspecific gravity lower than the specific gravity of a part between theposition at 20 mm from the tip of the writing element and the positioncorresponding to the middle of the overall length.
 18. The writingimplement according to claim 13 characterized in that the tip partand/or the back part is formed of a metal or a resin having a specificgravity lower than the specific gravity of a part between the positionat 20 mm from the tip of the writing element and the positioncorresponding to the middle of the overall length.
 19. The writingimplement according to claim 14 characterized in that the tip partand/or the back part is formed of a metal or a resin having a specificgravity lower than the specific gravity of a part between the positionat 20 mm from the tip of the writing element and the positioncorresponding to the middle of the overall length.
 20. The writingimplement according to claim 15 characterized in that the tip partand/or the back part is formed of a metal or a resin having a specificgravity lower than the specific gravity of a part between the positionat 20 mm from the tip of the writing element and the positioncorresponding to the middle of the overall length.